This application pertains to the art of ignition systems and more particularly to multi-power ignition systems. The invention is particularly applicable to ignitions for mobile heaters and will be described with particular reference thereto. It is to be appreciated, however, that the invention has broader applications such as ignition systems for water heaters, internal or external combustion engines, and the like.
Heretofore, ignition circuits have commonly included a silicone controlled rectifier (SCR) or other solid state switching devices in series with the primary winding of an ignition transformer to control the flow of current therethrough. Commonly, an oscillator or alternating power source forward and reverse biased the switching device such that a series of current pulses or oscillating current flowed through the primary winding. The secondary winding of the ignition transformer was connected with an ignition device for producing a corresponding series of electric discharges to ignite an air-fuel mixture.
For some applications, it is desirable to change the amount of power across the ignition device automatically in response to a preselected condition. Heretofore, to change the amount of power, an appropriate condition sensor was commonly connected with the gate electrode of the SCR or other solid state switching device to adjust its threshold voltage.
In heaters, particularly mobile heates, the ignition circuit is often powered by a battery. For example, supplemental heaters for trucks are often connected with the truck's battery. When the engine is not running, the supplemental heater draws power from the battery discharging it. In very cold climates where supplemental heaters are most needed to keep the contents of the truck or the engine of the truck warm, the truck battery tends to become discharged more quickly.